Pass environment variable to compiler

[saksmt]

I wasn't able to find a way to pass environment variable to compiler on build or test.
Neither --action_env has any effect, nor there is any parameter in scala_library/scala_binary/scala_test that can be used for that matter.

Motivation: there are some macros that are configured through environment variables which need to be set on compile time, specifically scalactic. Probably it should be fixed in scalactic itself, but with 3.1.x it seems easier to fix it in rules_scala than try to migrate from older versions and there may be other plugins with same behavior anyway.

As I could understand code in rules_scala it looks not so hard to fix (but I may be wrong since I'm not really familiar with the codebase) by just passing additional argument from scala_* (say named compiler_env all the way to invocation of compiler. As for --action_env it may even be better but I don't really know how it works and more specifically why it doesn't.

[ittaiz]

We try heavily not to use environment variables since that seriously limits cache sharing. Why does this need to be an environment variable? Is this value constant but the only supported input mechanism is via env variable?

[saksmt]

Yeah it is constant in a way that it should not be changed between builds. It just controls macro expansion. Example of such macro and fix that will actually work with rules_scala: scalatest/scalatest#1795. So compiler options are essentially the same thing in this case.

[ittaiz]

We had this in our .bazelrc during the migration from maven to bazel and we could access it in our tests easily:

test --action_env=BUILD_TOOL=BAZEL

Could you try and see if you can access it?
You said it doesn't work for you for tests or compilation so I'm trying to see if maybe you're misusing the existing idiomatic mechanism. If we'll find it works for tests but not for the compiler env I think it will be easier to triage.

Also- please expect delays due to corona and limited capacity

[saksmt]

It is not about time when tests are run, it is about time when tests are compiled. And currently there is no way of providing any env variable so that it would be visible by compiler

[ittaiz]

The line I gave you was an example. In bazel compilation and tests are both actions.
When you use --action_env=Key=Value you add this K/V to all actions the build is spawning (unless specific rules will explicitly provide an empty env var map).
As you can see we simply call ctx.actions.run in the link you provided originally which means we work with the bazel idioms.
Please try the above out to see if you can get it to work.
If not please open a PR with a repro

[ittaiz]

to be clear- AFAICT rules_scala is WAI.
A repro would help shed some light.

[ittaiz]

Closing since it sounds this is a usage problem.
Please Reopen if you think otherwise.